Isomorphic Strings
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Given two strings s and t, determine if they are isomorphic.Two strings are isomorphic if the characters in s can be replaced to get t.
All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character but a character may map to itself.
For example, Given "egg", "add", return true.
Given "foo", "bar", return false.
Given "paper", "title", return true.
Note: You may assume both s and t have the same length.
哈希表法
复杂度
时间 O(N) 空间 O(N)
思路
用一个哈希表记录字符串s中字母到字符串t中字母的映射关系,一个集合记录已经映射过的字母。或者用两个哈希表记录双向的映射关系。这里不能只用一个哈希表,因为要排除egg->ddd这种多对一的映射。
代码
public class Solution {
public boolean isIsomorphic(String s, String t) {
Map<Character, Character> map = new HashMap<Character, Character>();
Set<Character> set = new HashSet<Character>();
if(s.length() != t.length()) return false;
for(int i = 0; i < s.length(); i++){
char sc = s.charAt(i), tc = t.charAt(i);
if(map.containsKey(sc)){
// 如果已经给s中的字符建立了映射,检查该映射是否和当前t中字符相同
if(tc != map.get(sc)) return false;
} else {
// 如果已经给t中的字符建立了映射,就返回假,因为出现了多对一映射
if(set.contains(tc)) return false;
map.put(sc, tc);
set.add(tc);
}
}
return true;
}
}
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